Illustrated in FIG. 1 is a conventional packaged integrated circuit device 100. The integrated circuit (IC) device 100 may, for example, comprise a microprocessor, a network processor, or other processing device, and the IC device 100 may be constructed using flip-chip mounting and Controlled Collapse Chip Connection (or “C4”) assembly techniques. The IC device 100 includes a die 110 that is disposed on a substrate 120, this substrate often referred to as the “package substrate.” A plurality of bond pads on the die 110 are electrically connected to a corresponding plurality of leads, or “lands”, on the substrate 120 by an array of connection elements 130 (e.g., solder balls, columns, etc.). Circuitry on the package substrate 120, in turn, routes the die leads to locations on the substrate 120 where electrical connections can be established with a next-level component (e.g., a motherboard, a computer system, a circuit board, another IC device, etc.). For example, the substrate circuitry may route all signal lines to a pin-grid array 125—or, alternatively, a ball-grid array—formed on a lower surface of the package substrate 120. The pin-grid (or ball-grid) array then electrically couples the die to the next-level component, which includes a mating array of terminals (e.g., pin sockets, bond pads, etc.).
During operation of the IC device 100, heat generated by the die 110 can damage the die if this heat is not transferred away from the die or otherwise dissipated. To remove heat from the die 110, the die is ultimately coupled with a heat sink 170 via a number of thermally conductive components, including a first thermal interface 140, a heat spreader 150, and a second thermal interface 160. The first thermal interface 140 is coupled with an upper surface of the die 110, and this thermal interface conducts heat from the die and to the heat spreader 150. Heat spreader 150 conducts heat laterally within itself to “spread” the heat laterally outwards from the die 110, and the heat spreader 150 also conducts the heat to the second thermal interface 160. The second thermal interface 160 conducts the heat to heat sink 170, which transfers the heat to the ambient environment. Heat sink 170 may include a plurality of fins 172, or other similar features providing increased surface area, to facilitate convection of heat to the surrounding air. The IC device 100 may also include a seal element 180 to seal the die 110 from the operating environment.
The efficient removal of heat from the die 110 depends on the performance of the first and second thermal interfaces 140, 160, as well as the heat spreader 150. As the power dissipation of processing devices increases with each design generation, the thermal performance of these devices becomes even more critical. To efficiently conduct heat away from the die 110 and toward the heat sink 170, the first and second thermal interfaces 140, 160 should efficiently conduct heat in a transverse direction (see arrow 105).
At the first thermal interface, it is known to use a layer of thermal grease disposed between the die 110 and the heat spreader 150. Thermal greases are, however, unsuitable for high power—and, hence, high heat—applications, as these materials lack sufficient thermal conductivity to efficiently remove a substantial heat load. It is also known to use a layer of a low melting point metal alloy (e.g., a solder) as the first thermal interface 140. However, these low melting point alloys are difficult to apply in a thin, uniform layer on the die 110, and these materials may also exhibit low reliability. Examples of materials used at the second thermal interface include thermally conductive epoxies and other thermally conductive polymer materials.